1. Field of the Invention
The present invention relates to a method of presuming interior situation of process chamber and a storage medium, and in particular relates to a method of presuming interior situation of process chamber that presumes the interior situation of process chamber in which a wafer is accommodated and subjected to predetermined processing.
2. Description of the Related Art
There is known a substrate processing apparatus that has a process chamber in which a wafer as a substrate is accommodated and subjected to predetermined processing, for example, plasma processing. In the substrate processing apparatus, if predetermined processing is repeatedly carried out, particles arising from, for example, plasma processing become attached to surfaces of component parts inside the process chamber. It is necessary to remove these particles on a regular basis because they cause troubles in semiconductor devices manufactured from wafers.
Conventionally, dry cleaning has been frequently used as a method of removing particles from the interior of the process chamber. In the dry cleaning, particles are removed by, for example, sputtering surfaces of component parts using plasma produced from oxygen gas. In the dry cleaning, it is difficult to completely remove particles, and dry cleaning takes much effort because it is necessary to produce plasma. For this reason, in recent years, an NPPC (non plasma particle cleaning) sequence has been used as a method that does not use plasma (see, for example, Japanese Laid-open Patent Publication (Kokai) No. 2005-317900).
In the NPPC sequence, particles are separated from component parts and discharged from the process chamber using a gas impact force, a gas viscous force, and an electrostatic force. In general, the NPPC sequence is comprised of a gas impact force mode in which a predetermined gas, for example, N2 gas is suddenly introduced into the process chamber so as to produce a gas impact force, a gas viscous force mode in which the pressure in the process chamber is controlled to a predetermined pressure so as to produce a gas viscous force from the introduced N2 gas, and an electrostatic force mode in which a DC voltage is applied to the component parts so as to produce an electrostatic force between the particles and the component parts.
In the case that particles are removed from the interior of the process chamber by the dry cleaning or the NPPC sequence, it is necessary to recognize the interior situation of the process chamber, for example, the degree to which particles have been removed from the interior of the process chamber, and for this reason, the number of particles discharged from the process chamber (hereinafter referred to as “discharged particles”) is counted. Specifically, an exhaust pipe that communicates with the process chamber is provided with an ISPM (in-situ particle monitor) that detects particles using scattered light so as to count the number of particles flowing in the exhaust pipe. For example, if the number of particles counted by the ISPM reaches 0, it is presumed that almost all particles have been removed from the interior of the process chamber.
Moreover, if a problem or a particular event occurs in the process chamber, this has different effects on the respective modes of the NPPC sequence (specifically, the number of particles removed in each mode changes), and hence recognizing the number of discharged particles in each mode is considered very useful in presuming the interior situation of the process chamber.
However, the numbers of particles removed in the respective modes are superposed in the number of particles counted by the ISPM, and it is thus difficult to recognize the number of discharged particles in each mode. That is, there may be a case where the number of discharged particles counted by the ISPM when the NPPC sequence is carried out does not accurately reflect a problem occurring in the process chamber.
For example, in an experiment that was conducted by the present inventors before developing the present invention, the correlation coefficient between the number of discharged particles counted by the ISPM when the NPPC sequence was carried out and the number of particles attached to a surface of a wafer accommodated in the process chamber was as low as 0.0448.
It is thus difficult to accurately presume the interior situation of the process chamber even if the number of discharged particles counted by the ISPM is used as it is.